In the usual saccharification of starch, starch is once cooked to gelatinize, this gelatinized starch is liquefied by the action of .alpha.-amylase and, thereafter, glucoamylase is added to produce dextrose. This method, however, requires a large amount of energy for gelatinizing the starch prior to its saccharification. In order to minimize such energy consumption, extensive researches have been made particularly in recent years for amylase which can be applied directly to raw starch, that is, is capable of hydrolyzing directly the raw starch.
Such energy-saving starch saccharification is essential for the production of alcohol fuel from various starches as biomass sources. In connection with the alcoholic fermentation of raw starch, investigations by S. Ueda et al., Hayashida et al., Y. K. Park et al., and so on are known. S. Ueda et al. have long studied the alcoholic fermentation of raw starch using glucoamylase produced by Black Aspergillus, Asp. awamori (see S. Ueda & Y. Koba, J. Fermentation Technology, 58, No. 3, 237 (1980), and S. Ueda et al., Biotech. Bioeng., Vol. 23, 291 (1981)). Hayashida et al. report that amylase produced by Asp. awamori is more effective in the hydrolysis of raw starch than amylase produced by Asp. oryzae or malt amylase. Y. K. Park et al. report the studies on the alcohol fermentation of starch without gelatinizing starch, using glucoamylase produced by Aspergillus niger or Aspergillus awamori (see Biotech. Bioeng., 24, 495 (1982).
In the saccharification of raw starch using glucoamylases produced by Aspergillus niger, Aspergillus awamori, or fungus belonging to genus Rhizopus, some problems still remain unsolved. The most serious problem is that the rate of hydrolysis of raw starch of the above-described enzymes are seriously low compared with their rate of hydrolysis of gelatinized starch. In other words, their raw starch-hydrolyzing activity is seriously low although they have high enzymatic activity. Usually it is considered that enzymes capable of hydrolyzing raw starch at a rate of hydrolysis of about 1/30 of that for gelatinized starch are promising as raw starch-hydrolyzing enzymes (see S. Ueda, Workshop, Carbohydrate Sources and Biotechnology, page 25 (1982), held under the auspices of National Food Research Institute, Japan and sponsored by The United Nations University).
About 2,000 strains of microorganisms living in soil and on wood were isolated by us and examined to find those microorganisms satisfying the requirement that the ratio of the gelatinized starch-hydrolyzing degree to the raw starch-hydrolyzing degree is 10:1 or less. It has been found that some microorganisms satisfy the foregoing requirement. They are strains belonging to genus Chalara, and the properties of the enzymes secreted by them are similar to those of glucoamylases in respect of the mechanisms of enzyme reactions. These enzymes are active and stable in a slightly acidic region and have greatly higher raw starch-hydrolyzing activity compared with conventional glucoamylases; that is, the ratio of the gelatinized starch-hydrolyzing activity to the raw starch-hydrolyzing activity is from 3.5:1 to 5:1, which is greatly higher compared with those of the known glucoamylases. Hence it has been found that the saccharification of raw starch can be performed advantageously on a commercial scale by using the above-described enzymes.